We should not forget that BTC fell as low as $ 3,208 USD (Dec 15, 2018) from the highest price at the end of 2017: $ 20,089.00 USD (Dec 17, 2017).
Some reasons that I think of:
- As you said, the public's skepticism about "BTC bubble";
- Whales sold BTC for profit taking;
- Many ICO projects selling BTC have been raised to have money to implement the idea;
- Many ponzi projects failed, one of which was Bitconnect, which affected confidence in cryptocurrency, in which BTC was also affected.